The invention relates to a method for monitoring the wheels of a motor vehicle having an antilock brake system for fault states, in particular for incorrect tire pressures, the occurrence of a fault state and the wheel position of the wheel at which the fault state has occurred being indicated. In addition, the invention relates to a system for monitoring the wheels of a motor vehicle having an antilock brake system, for fault states, in particular for incorrect tire pressures, the system indicating the occurrence of a fault state and the wheel position of the wheel at which the fault state has occurred.
The term fault state is to be interpreted loosely in the present context and comprises all states which are considered to be worthy of detection.
With respect to the systems of the generic type and the methods of the generic type it is known, for example, that the wheel units transmit information to a central evaluation device, arranged on the chassis of the motor vehicle, by means of radio frequency signals. In their present context, wheel units are to be understood as any unit which rotates with a respective wheel and is suitable for supplying information or data by means of which fault states which possibly occur at the wheel can be detected. In addition to the actual detection of a fault state, provision is made in many systems and methods of the generic type for the wheel position (for example front left, front right, rear left, rear right) of the individual wheels to be determined, so that, when a fault state occurs, the fault state can be indicated together with the respective wheel position.
For example, EP 0 806 307 B1 has already disclosed a method for carrying out the assignment of the wheel position to air pressure monitoring devices in an air pressure monitoring system of a motor vehicle, the motor vehicle having, inter alia, the following components: a number of wheels, each wheel being assigned an air pressure monitoring device which is capable of transmitting an individual identifier to a central processor unit, and a central processor unit in which the assignment of the identifier to an air pressure monitoring device relating to the wheel position for each wheel is stored. In the method known from EP 0 806 307 B1, the assignment of the air pressure monitoring device to the wheel position is performed as follows: an assignment mode is switched on; the individual identifiers of the air pressure monitoring device are output; the central processor unit evaluates which individual identifier has been transmitted from which wheel position; the assignment which is determined in the central processor unit is stored; and the assignment mode is switched off and the air pressure monitoring system is operated in a pressure monitoring mode. In order to evaluate the individual identifiers, there is, in particular, provision here for a specific variable, for example the wheel speed, for each wheel of the motor vehicle to be measured both with a wheel unit of the air pressure monitoring device and with a fixed sensor with a known wheel position. Then, the wheel position of the individual wheels is determined by comparing the output signals of the fixed sensors and the output signals of the wheel units.
DE 197 20 123 C2 also discloses that a separate antenna is to be provided in the region of each wheel to be monitored, which antenna can be used to receive signals emitted by the wheel units. Although each of the antennas can, under certain circumstances, also receive signals from wheel units which are not arranged directly adjacent to the respective antenna, according to the teaching of DE 197 20 123 C2 it is sufficient, for determining the wheel positions of the individual wheels, to assume that a signal which is emitted and received by a directly adjacent wheel unit has a higher signal level than a signal which is received by a more remotely arranged wheel unit.
The known systems and methods have in common the fact that they are very complex and therefore expensive in terms of the hardware and software necessary to determine the wheel positions.